In some structures, it may be desirable to selectively adjust the surface characteristics. As a basic example, most aircraft wings include flaps, which may be engaged to modify the drag and lift characteristics of the aircraft. Additionally, projectiles such as cruise missiles often include adjustable control surfaces to modify the trajectory of the projectile in flight.
At the other end of the spectrum, the entire wing may be configured to adjust. For example, the Grumman F-14 Tomcat features a variable geometry wing design. This variable geometry wing design provides the F-14 with one aerodynamic surface configuration suited to low velocity as well as another configuration for high velocity. A mechanical system controls the disposition of the wings. Mechanically adjusting the control surface, however, disrupts the airflow, reducing aerodynamic efficiency and undercutting the benefit of the functionality.
Various other schemes for extending and dynamically changing wing and control surface configurations have been developed, but have various limitations. For example, many systems can only extend a relatively small amount before reaching a mechanical limit. In addition, many such systems create uneven airflow surfaces.
In addition to in-flight surface adjustments, an aerodynamic system may require an in-flight surface geometry which would be inappropriate for storage and/or launch of the system. For example, in projectiles which are fired from a tube, the internal geometry of the launch mechanism may place constraints on the use of canards. As such, canards are sometimes configured to stow inside of or flush with the projectile for deployment after launch. As with mechanically adjusted wings, deployable canards are generally actuated with mechanical systems, reducing reliability and increasing cost.